Here is a picture which shows the differences in the first three generations of frames quite well. If yours has a uniformly slight rough texture all the way around, it is a Gen1. If there is checkering or grooves on the front and rear of the grip, it is a Gen2.

Gen1 Glock 19s are not common, and might be worth a bit more than a normal used G19 to a Glock collector, especially if you have the box and original magazines/manual/etc.

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"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)